The present invention relates to a communication system performing routing control between circuit switched network and interconnection network comprising protocol for network communication.
ITU-T Recommendation H.323 may be utilized as a protocol for call control in an interconnection network (hereinafter called as internet) having network communication protocol like LAN, WAN or the Internet based on the IP networking technique. H.323 includes Q.931 protocol which is used as a call control signaling for establishing and releasing calls among terminal equipment and gateways in the internet, where the gateway is an equipment which interconnects between a call in the circuit switched network such as telephone networks, integrated services digital networks and mobile communication networks and a call in the internet. The network architecture in the H.323 includes a gatekeeper which performs functions of address translation, access control, bandwidth management, etc. The gatekeeper may have additional functions relating to the call control such as a conference call control.
In many cases, a public switched telephone network is constructed as Intelligent Network (IN) in order to provide enhanced and diversified network service. The IN is a network connection architecture recommended in Q.1200 series of ITU-T. Difference between conventional network and the IN are two points of independence and integration of the service control function from the switching equipment.
An aim of the conventional telephone switching system is to efficiently provide one to one communication services. However, in order to provide the service control function to each switching equipment, complex addition and modification on the function are required. Therefore, advancing of services is somewhat limited. The IN solves this problem by constructing a layered structure such that the switching equipment executes a basic call connection function and a dedicated information processing equipment executes a function for providing complex services. According to the IN, a service control function needed for realization, maintenance and operation of the network services is integrated and controlling, monitoring and managing of the call control part are performed so as to meet an introduction of advanced network services. Additional services such as freephone service, abbreviated dialing service, virtual private network service and transfer service are realized with the IN technique.
A part of structure of IN can be seen in FIG. 1. In the figure, a call control part 11 for performing only basic connection of a circuit such as a digital switching system, a service control part 12 for directing the service to the call control part 11, and a service control information database 13 for storing service control information are illustrated.
In a PBX and a private communication network composed mainly with dedicated line, these additional services are realized by adding a service control function to a server equipment connected to the PBX.
However, when a call for connecting to a telephone terminal in a telephone network is originated from an information terminal of the internet, it is not sure that the nearest gateway with respect to the called telephone terminal is always selected. The longer in distance between a selected gateway and the called telephone terminal, the less efficient use of communication resources due to wasteful routing. This invites an inconvenience to users in paying increased charge to the telephone networks.
Hitherto, the internet provides gatekeeper. When a call from an information terminal C1 of the internet to a telephone terminal T1 of the telephone network is arrived, the information terminal C1 inquires to the gatekeeper and thus the gatekeeper responds by retrieving a gateway address AG1 for the called telephone number NT1. Therefore, the gatekeeper has an address table to take the correspondence between the telephone number and the address of the gateway used to connect to the telephone number. The routing control can be thus performed by selecting the address of nearest gateway depending upon the called telephone number informed from the calling information terminal. However, for the Internet continuing self-increase, it is difficult to always renew the correspondence information in the gateway between the address of the gateway and the telephone number. Therefore, the inconvenience comes out from that communication resources cannot use efficiently for wasteful routing as mentioned above.
More concretely, an inconvenience may come out in case of usage of the call transfer service. For example, it is assumed that there is a service for transferring a calling to a telephone terminal T1 of the telephone network to an information terminal C2 of the internet is set, and that an information terminal C1 of the internet originates a call to the same telephone terminal T1 of the telephone network through the gateway. In this case, the service control part of the telephone switching system, which detects that the telephone terminal T1 is called, needs to execute a procedure for terminating the call to the information terminal C2 by transferring again the call into the internet through the gateway. Such wasteful procedure between the networks will produce further consumption of the communication resources. This problem is caused by that the one communication network has only information for call transfer to the other communication network. The similar problem will occur in case that a mobile terminal equipment to be called in the mobile communication network is roaming when a call is arrived to the mobile communication network from the internet.
Furthermore, even in case that a call to an information terminal of the internet is originated from a telephone terminal of the telephone network, it is not sure that the nearest gateway with respect to the called telephone terminal is surely selected.
It is therefore an object of the present invention to provide a communication system to embody the routing control using communication resources efficiently, at calling from one network to other network, in the network connection between a telephone network and internet.
According to the present invention, a routing control communication system includes a circuit switched network provided with a service control information database having a telephone numbers table, an interconnection network provided with a network communication protocol and an information terminal, and a network interworking equipment, such as a gateway, provided with one terminal connected with the circuit switched network and the other terminal connected with the interconnection network. The information database is connected with the interconnection network, and the information terminal of the interconnection network is constituted so as to obtain a transferred terminal number corresponding to a called telephone number from the service control information database.
Thus, when calling to the telephone terminal of the circuit switched network from the information terminal in the interconnection network, the information terminal can inquire directly whether there is a transferred terminal number corresponding to a called telephone number in the service control information database of IN facility. In case that the transferred terminal number corresponds to a telephone number (E.164) of the circuit switched network, it is possible to transfer the call to the address of an optimum gateway. Whereas, in case that the. transferred terminal number is an address of the interconnection network, it is possible to send a call directly to the address.
It is preferred that the information terminal of the interconnection network for obtaining the terminal number to be transferred includes a memory unit for storing relationship information between the received called telephone number and the transferred terminal number. Consequently, an information terminal is not necessary to inquire again to the same called telephone number. Since, however, the obtained information may become incorrect and thus the use of the information as a permanent one may cause misaddressing, then it is desired to use a cache memory for temporary storage of the information.
It is also preferred that the transferred terminal number identifies a telephone number of a circuit switched network, or an address of the interconnection network. It is possible to call the address of corresponding gateway if it is the telephone number of the circuit switched network. It is possible to directly call the address if it is the address of the interconnection network.
It is further preferred that the information terminal of the interconnection network for obtaining the transferred terminal number is a gatekeeper having an address table of the interconnection network, and that the service control information database is constituted so as to obtain from the gatekeeper a telephone number of a transferred gateway which corresponds to a called address. The routing control communication system which efficiently uses communication resources can be realized by communicating with each other for the service control information database having the telephone number table and the gatekeeper having the address table.
It is also preferred that a plurality of gateway telephone numbers to be transferred are obtained from the gatekeeper, simultaneously. Thus, the telephone network can select automatically with high priority gateway from the view point of quality service.
It is preferred that an interworking equipment is connected to the service control information database, and that the interworking equipment performs mutual signal exchange for enquiry/response signals. Thus, it is possible to use an existing IN facility or gatekeeper for a role of protocol conversion between the service control information database and the gatekeeper.
Preferably, the interworking equipment includes a memory unit for storing information relating to mutual signal exchange of enquiry/response signals.
It is also preferred that the circuit switched network includes an IN facility. Thus, since the service control information database can be separated from the switching equipment which is a call control part, the invention can be easily realized.
It is further preferred that the network control equipment is a gateway.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.